Cutting insert

ABSTRACT

A cutting insert for material-removing machining is formed with at least one transversely extending cutting edge, a transversely extending inner groove extending along and generally the full length of the cutting edge and having an outer edge and an inner edge spaced longitudinally from the outer edge and lying between the outer edge and the cutting edge, and an outer transversely extending groove extending along and generally the full length of the cutting edge and having an outer edge and an inner edge spaced longitudinally from the respective outer edge. The inner groove lies between the outer groove and the land. A transversely extending land surface extends immediately adjacent the cutting edge along the cutting edge between the inner groove and the cutting edge. A row of transversely spaced outer chip-forming elements lie wholly between the outer-groove outer edge and the inner-groove inner edge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/DE93/01109 filed 18 Nov. 1993 with a claim to the priority of Germanapplication G 92 15 855.2 filed 21 Nov. 1992.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US national phase of PCT applicationPCT/DE93/01109 filed 18 Nov. 1993 with a claim to the priority of Germanapplication G 92 15 855.2 filed 21 Nov. 1992.

FIELD OF THE INVENTION

The invention relates a cutting insert for material-removing machining,in particular drilling, with at least one cutting edge, a land offsettherefrom toward the center of the surface of the cutting insert, achip-forming groove extending full length parallel to the cutting edge,and along and parallel to the cutting edge separate chip-formingelements.

BACKGROUND OF THE INVENTION

Such cutting inserts are known for example from German 2,231,631. Thispublication also describes how premature breaking of the chips to formshort chips is effected by a concave groove or grooves which are eachformed arcuately or as semicircles seen in cross section. Above all theidea of a double groove is rejected as disadvantageous. For better chipbreaking at least one projection is provided near the corner in a singlegroove.

German 2,515,686 describes a cutting tool where extending from the landis a descending flank which if necessary can also be part of achip-breaking groove, rectangular or triangular shaped recesses beingprovided in the descending flank and extending to the region of theland. Raised part-spherical or frustoconical chip-forming elements withdifferent basic shapes are also seen in U.S. Pat. No. 4,214,845, thechip-forming elements each being raised relative to the cutting edge andextending past them. Frustoconical chip-forming elements with generallytriangular bases are seen in German 3,148,535, each being aligned to thebase-surface limiting line of the chip-forming element in the directionof the adjacent cutting edge.

European 0,208,668 describes a cutting insert with recesses that arearranged at least partially in the curved chip-breaking surface(chip-breaking groove) and that extend beyond the chip-breaking grooveinto the region of the adjacent land. In a corresponding way for exampleEuropean 0,168,555 or 0,222,317 describe cutting inserts with raisedcenters where semicircular projections extend from these raised centerstoward and beyond the cutting edge. Oppositely the raised middle part(plateau) is provided on its rising flank with cutouts as described inU.S. Pat. No. 4,880,338.

All the above-discussed embodiments are supposed to improve chipbreaking. The chip breaking basically relies on deforming the passingchip until it breaks. Chips that are of greater cross section are easierto break than skinny chips, and the chip thickness is above alldependent on the workpiece being machined or its composition. Furtherinfluence over chip breaking can be had via the curvature of the surfaceover which the chip passes. As the radius of the chip-breaking groovegets smaller the chip is more radically bent. The disadvantage of thisis that the machining force and the load on the indexable cutting plateis increased. The additional forces from chip breaking lead to undesiredvibrations in the machining process.

A further substantial possibility for influencing the chip is byimparting a crease to the chip cross section, either by bumps in theform of partial spheres, ribs, or the like or in the form ofcorrugations.

OBJECTS OF THE INVENTION

It is an object of the present invention to improve on the alreadydescribed cutting insert so that the surface topography of the cuttingsurface is set up for different cutting circumstances and differentworkpieces, and in particular the shape should facilitate faster feed aswell as a long tool service life.

SUMMARY OF THE INVENTION

A cutting insert for material-removing machining has a cutting surfaceformed with at least one transversely extending cutting edge, atransversely extending groove formation, a transversely extending landsurface, and a row of transversely spaced outer chip-forming elements.The groove formation, which can be formed by two parallel grooves,extends along and generally the full length of the cutting edge and hasan outer edge and an inner edge spaced longitudinally therefrom andlying between the outer edge and the cutting edge. The land surfaceextends immediately adjacent the cutting edge along the cutting edgebetween the groove formation and the cutting edge. The row oftransversely spaced outer chip-forming elements lie in the grooveformation wholly between the outer edge and the inner edge. If fast feedproduces a relatively thick chip with a high resistance, this stiffnessis further increased by the cup-shaped pits or bumps provided accordingto the invention. With relatively fast feed the chip engages the end ofthe second chip-forming groove without prior bending so that it isdeflected. The chip breaks here since the resistance moment of the chipwith higher feed rate is larger and thus, with the same bend angle ofthe chip, breaking takes place sooner. The succeeding chip-forminggrooves thus make high feed rates possible and one and the same tool canbe used to machine different materials with corresponding different chipformation during machining.

The service life of the cutting insert is of considerable meaning forsure machining. Recesses adjacent the cutting edge create a weakness andthe danger of premature breaking of the cutter. For this reason it is ofsignificance that the recesses are spaced from the cutting edge. Theoptimum is a spacing of the recesses from the cutting edge of 0.5 to 1times the feed rate (mm/revolution).

Combinations are recommended wherein in the region set back from thecutting edge of the second or back chip-forming groove there are furtherpits and/or bumps. In particular with combinations of recesses adjacentthe cutting edge with further recesses or bumps in the region remotefrom the cutting edge conditions are created whereby the chip issubjected to additional transverse forces, in particular when in thechip-travel direction the pits and/or bumps arranged one behind theother are offset laterally from one another. The transverse forcesproduced in this manner additionally promote chip breaking.

On the other hand the groove adjacent the cutting edge can have raisedchip-forming elements (bumps) which while they in fact uniformlyincrease the cutting forces also have the advantage of forming a chip.The chip is of corrugated shape which the mentioned offset arrangementof the chip-forming element in the groove remote from the cutting edgesubject them to additional transverse forces so that chip-breaking isenhanced.

In a further alternative embodiment of the invention at least two rowsof raised and/or groove-shaped chip-forming elements extendingperpendicular to the cutting edge in a single chip-forming groove andthat the chip-forming elements one behind the other are offset laterallyto each other. This embodiment also produces the above-describedadvantages of transverse forces during chip formation.

Finally according to a further embodiment of the invention two parallelto one another full-length chip-forming grooves are provided and raisedor groove-shaped chip-forming elements are provided in the transitionregion of the chip-forming grooves.

Preferably the chip-forming elements are of different sizes, whereby inparticular the chip forming elements in the region remote from thecutting edge are bigger than those near the cutting edge.

Preferably a cutting insert is used whose novelty is that each of thecutting corners bordering a main cutting edge has on the side of themain cutting edge an extension formed as a secondary cutting edge whichis generally parallel to or slightly inclined at an angle of at most 10°to the longitudinal bore-hole axis. The secondary cutting edge has theeffect that the bore-hole wall during advance of the cutter smooths thealready produced bore-hole surface. Since during drilling a cuttingcorner describes a spiral curve, without the extension according to theinvention there are in the bore-hole cross section two succeeding burrsat different positions which the secondary cutting edge smooths andremoves. It is significant that the secondary edge for this removalextends generally parallel to the bore-hole axis or under a slight anglethereto. The inclination should preferably not exceed 1° to 2° relativeto the bore-hole axis.

According to a further embodiment of the invention the length of theextension formed as a secondary blade corresponds generally to the feedlength of one revolution of the drill, preferably with small drills to20 mm bore-hole diameter up to 2/10 mm and with bigger drills to 60 mmbore-hole diameter up to 4/10 mm. The cutting-corner radius ispreferably 0.2 mm to 1.2 mm.

The cutting corner can in this arrangement either be completely roundedor formed by short cutting-corner regions in the form of a chamfering.

The inventive cutting inserts can have on their main cutting edge one ormore cutting corners. Preferably the cutting insert has at least twoprojecting cutting points per cutting edge so that a single indexablecutting plate has more than one cutting region for the chip, whichproduces better chip guiding. Such arrangement of this cutting plateleads also to better centering of the drill.

In particular according to a further feature of the invention the numberof cutting regions is correspondingly large. This means for an indexablecutting plate with two cutting points that two cutting regions areformed by means of which smaller-diameter chips are formed which latterduring drilling are easier to guide and easier to break.

According to a further embodiment of the invention each of the cuttingedges has a generally concave shape with a setback which is preferablyin the middle of the cutting edge. Unlike the conventional hexagonalcutting plate with obtuse angles between adjacent cutting edges in theshape of a "protuberance" according to the invention the middle of thecutting edge is offset backward relative to a line drawn between twoadjacent cutting corners so that two cutting regions are created foreach cutting edge. Preferably the setback produces two cutting-edgeportions which have an outside angle of less than 176°. In particularthis angle lies between 145° and 170°.

The cutting points of such a cutting edge can be formed by the cuttingcorners or adjacent cutting-edge portion halves. In both cases thecutting corners of such a cutting edge are near the corner. If thecutting point is formed by a cutting corner, it should be rounded. Acutting corner near the corner region can preferably be such that thecorner has an enlarged corner angle. In this manner preferably the twocorner points of a cutting edge are arranged somewhat in the respectivecutting corner halves near the corners.

Cutting inserts of rhombic or triangular shape with a nose portion inone of the cutting corners or at least one main cutting edge connectedwith the nose portion wherein the nose portion is elongated in the ridgedirection at an acute-angle cutting corner and which is formed by aplurality of curves segments which are arranged symmetrically to acenterline of the cutting corner are indeed known from European0,162,029 but this cutting insert serves special, here not claimed, usessuch as longitudinal turning, inside finish turning, reliefgrinding/turning, and outside finish turning. With this cutting insertthe nose portion serves only as a shortened effective cutting edge sothat this cutting insert is usable only for the intended purposes, nothowever for drilling.

Furthermore preferably the spacing of the setback from the cutting pointlies relative to a vertical to connecting line of the cutting corners inthe region between 0.1 mm and 1.8 mm. This spacing is intended to meanthe spacing between two parallel lines one of which is drawn between thebottom of the setback and the other through the tops of the cuttingpoints and which run parallel to a line connecting the cutting corners.

Preferably each cutting edge is formed axial symmetrical with respect toa perpendicular through its center.

The region of the described setback can be formed by appropriateformation of the cutting-plate side surfaces in the corners it ispreferably rounded. In particular the cutting insert should be generallytriangular or rectangular (seen in top view) and/or formed as anindexable cutting plate.

With respect to the formation of the side surfaces or free surfaces forforming a free angle as well as of the cutting surface one can reachback basically to the embodiments known form the art. The cuttingsurface can for example have adjacent the cutting edge a land and/or achip-breaking groove as well as chip-forming elements.

In addition the present invention can also be embodied in such cuttinginserts wherein the main blade is interrupted such that the cutting edgehalves form an obtuse angle at the interruption. Even in this embodimentthe cutting corner defining the cutting edge halves is formed with anextension serving as secondary cutting edge, the secondary cutting edgebeing generally parallel to a bisector of the obtuse angle or thebore-hole central axis or slightly inclined to one of these lines.

In particular according to a further embodiment of the invention suchcutting inserts are claimed which have seen from above on the cuttingsurface a generally rectangular shape with two opposite side surfaceswith their cutting edges so interrupted in the middle at their cuttingpoints that they form an obtuse angle at the interruption and that eachof the four formed cutting corners has an extension forming an auxiliarycutting edge which forms a projection relative to the longer sidesurface and that extends at an acute angle in the longitudinal sidesurfaces. The rectangular cutting-plate shape is known basically forexample from European 0,181,844 but it lacks the cutting cornerslimiting the active blades at an auxiliary cutter that serves forsmoothing the interior wall of the bore hole. According to the presentinvention there are no projections as in the cutting insert according toEuropean 0,181,844 that form an acute angle with the long side surfaces,but the cutting corner has an actual secondary cutter before it forms anacute angle of preferably 15° to 25° to the side surfaces notconstituted as cutters.

Preferably the cutting insert has a generally triangular or rectangularform and/or is formed as an indexable cutting plate.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a top view of a cutting insert according to the invention witha basically rectangular shape;

FIG. 1a is a partial section taken along line Ia--Ia of FIG. 1;

FIG. 1b is a sectional partial view of a cutting insert showing thepassing chip in three succeeding positions;

FIG. 2 is a top view of an alternative embodiment of a generallyrectangular cutting insert;

FIG. 2a is a partial section taken along line IIa--IIa of FIG. 2;

FIGS. 3 and 4 show other basic shapes of a rectangular cutting insert;

FIG. 5 is a sectional view of a drilling tool in use with three cuttinginserts according to the invention;

FIG. 6a is a sectional view of a drilling tool;

FIG. 6b is an end view of the drilling tool according to FIG. 6a; and

FIGS. 7a and 7b are partial sections of a cutting insert advancing in adrill hole.

SPECIFIC DESCRIPTION

The cutting insert 10 shown in FIG. 1 is basically rectangular with fourcutting corners 11 which define the cutting surface as well as thecutting edges 13. As known in the prior art the cutting insert has amounting hole 14. Each of the two opposite cutting edges 13 has acentral depression 15 as well as symmetrically flanking the depressiontwo cutting points 16a and 16b which here are rounded. Outside eachcorner 11 the cutting insert has extensions 17 which extend along thebore-hole axis or the here shown longitudinal axis L. These extensions17 serve during boring as secondary cutting edges as described withreference to FIGS. 7a and 7b. The auxiliary cutting edge 17 has a lengthwhich corresponds generally to the advance length during one revolutionof the drill, here in the neighborhood of 4/10 mm. A land 19 which runsat an angle up to 25° bridges the long side surfaces 18.

As visible from FIG. 1a, the cutting insert has adjacent a land at thecutting edge 13 two immediately adjacent chip-forming grooves 45 and 46extending parallel to the cutting edge 13. The first chip-forming groove45 has pits 47 which as seen from above are circular or, as shown, oval.The second chip-forming groove 46 has bumps 48 (raised chip-formingelements) which are of part-spherical shape and of greater diameter thanthe individual upstream chip-forming elements 47. Variations arepossible where the pits or bumps in the two chip-forming grooves 45 and46 are reversed, as shown in FIG. 1 there are bumps 48 in the firstchip-forming groove and pits in the second chip-forming groove 46. Thechip-forming elements 47 and 48 are offset from each other which isshown in FIG. 1 with reference to the maxima and minima.

FIG. 1b shows three longitudinal sections through the passing chip oncontact with the chip-forming elements near the cutting edge, that isthe pits 47, as well as on contact with the chip-forming element remotefrom the cutting edge, the bumps 48 as well as in a position free of thecutting surface. A double groove 45, 46 is formed adjacent the land 50in the present case so that the cutting surface is shown in perspectivein order to make the chip-travel direction (arrow 54) clear. FIG. 1b inparticular makes clear that the bumps 48 are somewhat laterally offsetin the chip-travel direction from the pits 47 so that the chip as itcontacts the chip-forming elements remote from the cutting edge issubjected to an additional lifting or bending.

FIG. 2 shows a variation on the described cutting insert. This cuttinginsert is in contrast to the cutting insert according to FIG. 1 notelongated but square with the cutting insert 20 having once again fourcutting corners 21 with intervening cutting edges 22 whose cutting-edgepartial portions 22a and 22b form an angle a of about 160° to eachother. Thus per cutting edge in the corner region there are two cuttingpoints 23 which form a cutting-corner angle c of about 70°. An extension17 is formed from the cutting edge 23. The cutting insert ismirror-symmetrical to the longitudinal axes L₁ and L₂. The sectionaccording to line IIa--IIA according to FIG. 2a shows that there is afirst chip-forming groove 51 at the land 50, then a ridge 52 at the sameheight as the land 50 on which there are raised chip-forming elements 49whose size is such that they project into the front chip-forming groove51 as well as into the further chip-forming groove 53 arranged behindthe ridge 52 parallel to the cutting edge 13.

Further embodiments of the cutting insert are shown in the following,for clarity's sake without chip-forming elements whose shape can be theknown from the state of the art in particular as known from thereferences cited in the introduction.

An embodiment of the cutting insert according to FIG. 2 is seen in FIG.3. Even here there is axial symmetry to the axes L₁ and L₂ but thecutting insert 24 has no rounded points 16a and 16b or 23 but respectivepoints 25 which are each arranged at an angle d of about 160° from theouter portion of the main cutting edge. The extensions 17 are hereconvexly curved without violating the principles of the invention ofusing these extensions 17 as slide surfaces.

The cutting insert of FIG. 4 corresponds generally to the cutting insertaccording to FIG. 1 and is also formed as an elongated rectangle. Eachof the cutting edges 29 which extend mirror-symmetrically to atransverse axis L₃ has a cutting point 28 which is central and forms anobtuse angle. The side surface abutting the cutting edge 29 iscorrespondingly interrupted. Even in this embodiment the cutting edge 29has on each cutting corner an extension 17 which is aligned parallel tothe drillhole longitudinal axis or to the longitudinal axis L₄.

A drilling tool according to the invention that is equipped with twocutting inserts 20 as in FIG. 2 is shown in FIG. 5. A shaft 26 carrieson each of its opposite bit halves a respective cutting insert 20' or20" with the working regions of these cutting inserts overlapping as isshown on the right bit half in dot-dash lines for the cutting insert20". The bit seats are offset by 180°. The inner cutting insert 20'extends slightly past the bit longitudinal axis and is, with respect toits perpendicular, tipped at an angle b of about 5° to the connectingline of the cutting corner defining the effective cutting edge withrespect to the shaft longitudinal axis like the correspondingperpendicular of the other cutting insert. The cutting insert 20" isalso set back somewhat, about 0.1 mm, with respect to the cutting insert20'. During drilling in solid material 30 on contact of the bit theblade s₁₁ or the inner cutting corner of the bit contacts the workpiece30 first. According to what angle b was selected for the two cuttinginserts and the extent of the setback v₁ of the outer cutting insert 20"relative to the inner cutting insert 20' the first cutting edge s₂₁ ofthe outer cutting insert 20" leads with its point the point of theparticle-cutting region s₁₂ by the distance v₂ which also corresponds to0.1 mm. In each cutting insert 20' and 20" the respective cuttingregions s₁₁ and s₁₂ or s₂₁ and s₂₂ form guide surfaces so that duringdrilling there are altogether two chips per cutting-insert plate.

A cutting insert according to the embodiment shown in FIG. 1 is shown inFIGS. 6a and 6b. The cutting insert 31 has two cutting edges 32 onopposite sides, one of them having in the cutting edge center a concaveshape. Widening of the cutting corners 33 forms two cutting points 34per cutting edge 32 which are formed rounded. The 180° offset mountingposition of the cutting inserts 31 and 35 is shown in FIG. 6b. Bothcutting inserts 31 and 35 have their central longitudinal axes 36 tippedrelative to the bit-longitudinal axis 37 by an angle of 5°. The longside surfaces 38 of the cutting inserts 31 and 35, which are notconstituted as cutting edges, can be of the same size or longer than thecutting edge 32.

The operation of the extensions 17 is seen in FIGS. 7a and 7b. Thecutting insert shown partially in FIG. 7a is advanced on drilling insolid metal by a drill advance f with the positions of the cuttinginserts being shown at 39' and 39" after one revolution of the bit. Thecutting corner 40 of this cutting insert describes during bit advance anactual helix that forms a burr 41 whose size is determined by thecutting-corner angle. Reference 42 shows the respective drilled-holeaxis. On use of a cutting insert according to the invention andcorresponding to the representation of FIG. 7b the extension smooths theburr extension 41 while the remaining burr 43 is so small as almost todisappear.

We claim:
 1. A cutting insert for material-removing machining, theinsert being formed with:at least one transversely extending cuttingedge; a transversely extending inner groove extending along andgenerally the full length of the cutting edge and having an outer edgeand an inner edge spaced longitudinally from the outer edge and lyingbetween the outer edge and the cutting edge; an outer transverselyextending groove extending along and generally the full length of thecutting edge and having an outer edge and an inner edge spacedlongitudinally from the respective outer edge, the inner groove lyingbetween the outer groove and the cutting edge; a transversely extendingland surface extending immediately adjacent the cutting edge along thecutting edge between the inner groove and the cutting edge; and a row oftransversely spaced outer chip-forming elements lying wholly between theouter-groove outer edge and the inner-groove inner edge.
 2. The cuttinginsert defined in claim 1 wherein the elements are bumps.
 3. The cuttinginsert defined in claim 1 wherein the elements are recesses.
 4. Thecutting insert defined in claim 1 wherein the elements are wholly in theouter groove, the insert further comprising:a row of transversely spacedinner chip-forming elements lying wholly in the inner groove between therespective outer edge and the respective inner edge.
 5. The cuttinginsert defined in claim 4 wherein the elements in the outer groove areformed differently from the elements in the inner groove.
 6. The cuttinginsert defined in claim 5 wherein the elements in the outer groove arebigger than the elements in the inner groove.
 7. The cutting insertdefined in claim 5 wherein the elements of one of the rows are bumps andthe elements of the other of the rows are recesses.
 8. The cuttinginsert defined in claim 1 wherein the elements are mainly between theouter groove and the inner groove.
 9. The cutting insert defined inclaim 1 wherein the insert is formed with a pair of cutting corners eachhaving one side defined by the cutting edge and an outer side formedwith a longitudinal extension having a surface extending generallyperpendicular to the cutting edge.
 10. The cutting insert defined inclaim 9 wherein the outer side surfaces extend at an angle of between 1°and 2° to a longitudinal axis of the insert.
 11. The cutting insertdefined in claim 9 wherein the corners are circularly rounded and have aradius of curvature of between 0.2 mm and 1.2 mm.
 12. The cutting insertdefined in claim 9 wherein the one sides are straight.
 13. The cuttinginsert defined in claim 9 wherein the cutting edge has a center recessbetween the one sides.
 14. The cutting insert defined in claim 9 whereinthe one sides extend at an angle of between 150° and 170° to each other.15. The cutting insert defined in claim 14 wherein the one sides meet ata location spaced between 0.1 mm and 1.8 mm longitudinally behind astraight line joining the two corners.
 16. The cutting insert defined inclaim 9 wherein the insert is symmetrical about a longitudinal axisequidistant between the corners.
 17. The cutting insert defined in claim9 wherein the cutting insert has two such cutting edges directedlongitudinally oppositely and formed with respective such grooves andelements, the insert being symmetrical to a transverse axis extendingtransversely midway between the two edges.
 18. The cutting insertdefined in claim 9 wherein the one sides form an obtuse angle and alongitudinally forwardly directed central point.
 19. The cutting insertdefined in claim 9 wherein the insert has longitudinally inset sideedges set in from the extensions and with surfaces extending at an angleof between 15° and 25° between each of the side edges and the respectiveextension.
 20. A cutting insert for material-removing machining, theinsert being formed with:at least one transversely extending cuttingedge; an inner transversely extending groove extending along andgenerally the full length of the cutting edge and having an outer edgeand an inner edge lying between the respective outer edge and thecutting edge; an outer transversely extending groove extending along andgenerally the full length of the cutting edge and having an outer edgeand an inner edge spaced longitudinally therefrom and lying between therespective outer edge and the inner groove, the inner groove lyingbetween the outer groove and the cutting edge; a transversely extendingland extending immediately adjacent the cutting edge along the cuttingedge between the inner groove and the cutting edge; and a row oftransversely spaced outer chip-forming elements lying mainly between theouter groove and the inner groove and wholly between the outer-grooveouter edge and the inner-groove inner edge.